Posterior corneal stability after small incision lenticule extraction with different optical zones

BACKGROUND: To assess the changes in the posterior corneal surface following small incision lenticule extraction (SMILE) with different optical zones. METHODS: In this retrospective study, 106 eyes of 106 patients who underwent SMILE were recruited 3 years after the procedure. Eyes were divided into two groups according to the size of the surgical optical zone: group A (52 eyes, <= 6.2 mm) and group B (54 eyes, >= 6.5 mm). Posterior central elevation (PCE) and 12 other points at 45 degrees, 135 degrees, 225 degrees and 315 degrees with distances of 1 mm, 2 mm and 3 mm from the centre were recorded from Pentacam. RESULTS: No iatrogenic keratectasia was identified, and eyes in the two groups showed comparable visual results. The overall trend in posterior corneal elevation changes was consistent for both groups. PCE decreased significantly from 1.33 +/- 2.32 to 0.75 +/- 2.41 in group A (P = 0.024) and from 0.87 +/- 2.61 to 0.06 +/- 2.74 in group B (P = 0.003). All points in the central 2 mm region in both groups were reduced postoperatively. In the 4 mm and 6 mm corneal annulus, almost all points at 225 degrees and 315 degrees showed backward displacement, with the most prominent change occurring at 315 degrees in the 6 mm annulus (P < 0.001), indicating no forward protrusion in the inferior area. CONCLUSIONS: No forward protrusion in the posterior corneal surface was observed 3 years after SMILE with different optical zones. Comprehensive preoperative measurements are essential for ensuring corneal stability and avoiding iatrogenic keratectasia.